The invention relates to a joint for unfolding and locking a solar generator or a reflector, or other aerospace components that can be unfolded.
Solar generators or reflectors constitute unfolding systems of single, flexible segments, by way of example, which are unfolded in space after a transport phase is completed, for example. The unfolding can be performed by spring-powered or motor-powered unfolding joints, by means of which the individual segments can be directly connected, or by means of which rigid booms which act on the segments are connected. Such known joints have a very high unfolding torque at the start of the unfolding of a solar generator or reflector, the same being able to pivot about 180°. As a result the system components are subjected to high loads. Towards the end of the unfolding, known joints have a relatively low torque that is not sufficient to fully unfold the solar panel or the reflector in adverse conditions.
In order to ensure that approximately the same unfolding torque is applied over the entire duration of the unfolding, German patent document DE 196 49 741 A1 discloses a joint wherein it is possible, as a result of the shape of a sliding curve, to store part of the unfolding energy of a coil spring providing the drive, in a first half of the unfolding, in a yoke spring, and to direct this stored energy during the second half of the unfolding back to the movement via the control curve. German patent document DE 100 23 852 A1 discloses a joint consisting of two half joints, an axis of rotation, and a drive, wherein the drive has a drive spring designed as a constant force spring that generates a nearly constant torque during the unfolding, over the entire unfolding range. The loads on both the system components and the joint are reduced as a result of the approximately even unfolding torque. Moreover, interference torques on the axis are also reduced. In particular, impact forces arising during the unfolding are reduced. Because there is a greater unfolding torque even in the end position, the same typically characterized by a locked position, the joint bearing is under continuous compression force, such that a joint unit is ensured which has no play.
In practice, neither constant force springs nor other drives are yet capable of providing truly even unfolding torque. This is due to the fact that, among other things, it is not possible to take into account, and compensate for, frictional torques arising during the unfolding of the joint, over the unfolding process. The frictional torque is produced by electrical conductors of the solar generator or reflector that are routed across joint axes for the purpose of transmitting the electrical power, and which must be “bent” during the unfolding. As a result, the risk still exists that the rotary movement of the segments of the solar generator or reflector is suddenly halted once the unfolded position is reached, as the result of a locking of the joint. As a result, high “locking torques” are created, and must be taken into account when the size of the segments of the solar generator or reflector is designed. Moreover, there is a risk of loads on the unfolding mechanism that are too high. Particularly at the beginning and at the end of the unfolding, the load on the materials of the individual components is the greatest, such that the same is significant in the design of the sizing of the components.
Exemplary embodiments of the present invention provide a joint for unfolding and locking a solar generator, a reflector, or other aerospace components that can be unfolded, particularly for use in space, wherein the joint reduces the material load on the individual components.
The invention provides a joint for unfolding and locking a solar generator or a reflector, or other aerospace components which can be unfolded, consisting of two half joints, a joint axis, and a drive. According to the invention, a drive spring of the drive has a progressive characteristic curve over the unfolding angle of the two half joints, which increases over the unfolding, for the purpose of compensating a frictional torque that varies over the unfolding angle.
It is possible to take into account, and compensate, the frictional torque that increases over the unfolding angle as a result of a progressive spring characteristic curve. As a result, there is a mitigation in the reduction of the locking torque in the so-called partial unfolding, wherein only each of the outermost segments is opened by 90° for the transfer orbit. Moreover, there is a reduced load on the components and materials during the full unfolding of the segments of the solar generator or reflector. A further advantage is that it is possible to extend a joint used according to the invention to multiple unfolding axes. As a result of the frictional torques being taken into account over the spring characteristic curve, particularly those resulting from the wiring, it is also possible to accept and compensate for higher frictional torques due to other wiring at higher power output.
It is advantageous if the spring characteristic curve is selected in such a manner that the same corresponds over the entire unfolding angle to at least a predetermined multiple of the frictional torque, particularly to the triple of the frictional torque of the half joints rotated against each other. It is particularly advantageous if the spring characteristic curve is selected in such a manner that the same corresponds over the entire unfolding angle exactly to a predetermined multiple of the frictional torque, particularly to the triple of the frictional torque of the half joints rotated against each other. As a result, it is ensured that even in a “worst case” scenario, the opening torque is sufficiently high compared to the sum of all frictional torques.
In a further preferred embodiment, the drive is based on a constant force spring B-motor wherein the drive spring is arranged on a drive roll and a fixed end of the drive spring is fixed to the drive roll, and a free end of the drive spring runs around the joint axis. The drive spring has a shape that is other than a rectangular shape when it is extended to provide a progressive spring characteristic curve. The drive spring is arranged on and/or in the constant force spring B-motor in such a manner that it is wider facing inward. As a result, the spring torque constantly increases over the unfolding process.
According to an alternative or additional embodiment, the drive spring has a trapezoidal shape that is narrower towards its free end. According to the desired spring characteristic curve, the contour of the drive spring can also have other shapes which deviate from the preferred trapezoidal shape.
According to a further alternative or additional embodiment, the natural radius of the drive spring is greater towards its free end. In this embodiment the drive spring can be arranged on a non-circular drive roll or a non-circular supply roll, which rotates about the joint axis. As a result of the curve profile, meaning the radius, the drum is able to influence the spring torque in the desired manner.
According to a further alternative or additional embodiment, the drive spring is formed from multiple leaves of different lengths. The drive spring consists of a number of individual leaves. In order to achieve the progressive spring characteristic curve, different leave lengths are selected such that only a few—for example at least one—spring leaves are active at the beginning of the unfolding. The more the joint opens, the more spring leaves become active, which in turn leads to the increasing spring torque. The overall characteristic curve in this case will have a more step-like profile, in contrast to a trapezoidal embodiment of the drive spring.
In addition, the drive spring can have one or multiple recesses along its center line.
Because of constructive considerations, it is not possible to regulate the speed of the unfolding of the solar generator or reflector. In conventional joints, as a result, there is a high speed at the moment of the locking, particularly during the partial unfolding, wherein only each of the outermost segments is opened by 90° for the transfer orbit. The locking torque created in principle in the process can be reduced by the joint according to the invention because the drive spring releases comparably less energy up to this angular position.
As a result of the progressive characteristic curve that releases the same torque at the start of the unfolding as the drive mechanisms known to date, the load on the components, with respect to their strength, is not higher than before. However, due to the progressive spring characteristic curve, a significantly higher spring torque is obtained at the end of the unfolding. As a result, higher frictional torques from the wiring are acceptable. The characteristic curve in this case is selected in such a manner that, at the end of the unfolding, it corresponds to the predetermined multiple, particularly the triple, of the frictional torque.